1. Field of the Invention
The present invention relates to a ceramic turbine rotor adapted for use in a supercharger of an internal combustion engine, and more particularly to a machining method of the ceramic turbine rotor.
2. Discussion of the Prior Art
In recent years, various component parts of internal combustion engines for automotive vehicles tend to be made of ceramic materials for enhancing the performance of the engines. In a machining process of a ceramic turbine rotor adapted for use in a supercharger of the engine, it is required to bring precisely the turbine rotor on-center for finishing the turbine blades. For such requirement, as shown in FIG. 7(a), a conventional turbine rotor 1 is formed at its hub portion 3 with a center hole 9 for engagement with a spindle 14a of a headstock and connected to a metallic support shaft 5 which is formed at its one end with a center hole 9 for engagement with a spindle 14a of a tailstock. Alternatively, as shown in FIG. 7(b), the conventional turbine rotor 1 is formed at its hub portion 3 with a conical projection 15 for engagement with a tapered center hole 16 in the spindle 14a of the headstock. In the former case, the ceramic turbine rotor is apt to crack at its center hole 9. If the presence of crack is not detected, the ceramic turbine rotor will be damaged during the machining process or actual use thereof. In the latter case, the conical projection 15 of the ceramic turbine rotor is apt to break during the machining process. If the conical projection of the turbine rotor remains after the machining process and is broken during the following assembly process the rotational balance of the turbine rotor will deteriorate.